U.S. Pat. No. 4,928,146 issued to Yamada on May 22, 1990, is illustrative of a number of references which show the development of a series of electrostatic images carried on a photoconductive drum with different colored toners at a single development position. See also, U.S. Pat. No. 3,797,930, Tanaka et al, issued Mar. 17, 1974; U.S. Pat. No. 4,275,134, Knechtel, issued Jun. 23, 1981; Japanese Kokai 1-244477 (1989); U.S. Pat. No. 4,728,983, Zwaldo, issued Mar. 1, 1988. A series of four development stations are moved one after another to the development position. Each station develops an image and is replaced by another station as the series of stations is indexed to apply a different color toner to the next image. The series of stations are arranged side-by-side and moved linearly through a position in which the station to be used is aligned with the development position. After or as it is aligned, a cam is rotated to push the entire station toward the development position, generally moving transverse to the motion of the series of stations. Other references show the stations arranged on a rotary support with the stations being rotated through alignment with the development position.
This general approach has the advantage of utilizing only a single development position for applying four different color toners to electrostatic images. This permits the use of development stations whose size and number would prohibit them being spaced around the periphery of a relatively small photoconductive drum. It thus also permits the use of a small photoconductive drum in multicolor imaging. The use of a small drum has many advantages including reduced expense, reduced size of the apparatus and convenience in cartridge type replacement.
The structure shown in the prior art requires two motions on the part of each development unit. The four units are moved as one linearly in one direction and the unit opposite the development position is moved relative to the others transverse to that motion into operative relationship with the photoconductive drum. This second movement requires that the units be mounted so that they are movable relative to each other and also requires a separate moving mechanism for moving them, which moving mechanism must be properly timed and driven, and must be powered sufficiently to move an entire unit.
U.S. Pat. Nos. 4,922,302, issued to Hill et al, on May 1, 1990; 4,884,109, issued to Hill et al, on Nov. 28, 1989; and 4,797,704, issued to Hill et al, on Jan. 10, 1989; show a development station having an applicator with a rotating magnetic core and a stationary nonmagnetic sleeve around which a developer mixture is moved by rotation of the core to pass the developer through a development position. The applicator is fed by a rotating paddle positioned below the applicator which both mixes developer and supplies it to the applicator. Toner is periodically supplied to the mixture from a toner supply portion of the station. New toner is supplied by replacing the station.